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MAGNETIC-RESONANCE DETERMINATION OF THE ELECTRONIC DENSITY OF STATES AND THE METAL NONMETAL TRANSITION IN THE LAH2-LAH3 SYSTEM

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Abstract

Proton spin-lattice relaxation rate R1 and La-139 Knight shift measurements have been utilized to study the electronic density of states N(E(F)) at the Fermi level and the metal-non-metal (MNM) transition in the lanthanum hydrides, LaH(x)(2 less-than-or-equal-to x less-than-or-equal-to 3), in samples prepared from highest purity Ames Laboratory lanthanum as well as from lanthanum containing controlled low levels (less than 300 ppm) of gadolinium. In the pure samples, free-electron-like metallic behavior is found for all compositions up to x almost-equal-to 2.8 at temperatures T less-than-or-equal-to 200 K. In the gadolinium-doped samples the Gd3+ ion spin fluctuations, characterized by the ion spin-lattice relaxation time tau-i, contribute an additional proton spin relaxation rate. Measurements of this rate for x < 2.8 show that tau-i is-proportional-to T-1 at all temperatures, indicating metallic behavior. However, for x greater-than-or-equal-to 2.8 and T > 250 K, tau-i is-proportional-to T-5, showing that Gd3+ spin relaxation is then governed by the two-phonon process typical of insulating solids

Topics: QD, TN
Publisher: ELSEVIER SCIENCE SA LAUSANNE
OAI identifier: oai:wrap.warwick.ac.uk:22478
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